132 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURD 
trance chamber. In the smaller limbs the galleries extend obliquely 
around the limbs and may completely encircle them. They are 
frequently very abundant in ash cordwood. 
The oak bark beetles (Pseudopityophthorus spp.) 1m some instances 
attack so heavily as to cause the death of weakened oak trees. 
Usually, however, these beetles confine themselves to injured, felled, 
or recently killed trees or to the dead branches and twigs of other- 
wise healthy trees. The adults are tiny, cylindrical, brown bark 
beetles. Their typical work consists of transverse egg galleries ex- 
tending for a short distance on either side of the central entrance 
tunnel and diverging larval mines running longitudinally with the 
trunk or limb. 
The mountain mahogany bark beetle (Renocis heterodoxwus Csy.) 
is a small brown bark beetle that mines the limbs and trunks of 
mountain mahogany in Oregon, Nevada, and California. 
The shrub bark beetle (Micracis hirtellus Lec.) is a secondary 
species which mines the hard, dry wood of many flowering shrubs 
and broadleaved trees including willow, alder, and laurel in Cali- 
fornia. The adults are dark reddish brown and about one-eighth 
inch long. They have been found boring into lead telephone cables. 
The birch bark beetle (Dryocoetes betulae Hopk.) is a secondary 
enemy of birch throughout British Columbia, Canada, and the 
northern part of the United States. 
FLATHEADED BORERS 
(Buprestidae) 
The flatheaded or metallic wood borers (7/2) comprise a large 
family of beetles the larvae of which mine in the inner bark and 
wood of many species of forest trees. Their activities are diversified. 
A few species attack and kill healthy trees by mining under the bark; 
others bore into the inner bark and sapwood of trunks, branches, and 
twigs of weakened and dying trees; while others breed only in dead 
or recently felled trees and make flattened, winding wormholes 
through the wood. A few species are leaf miners. In general, the 
group is a destructive one in that they sometimes kill living trees 
and often reduce the value of lumber by their attacks. Others assist 
materially in the natural process of disintegrating deadwood in the 
forest, and these are decidedly beneficial. 
The adults are flattened, frequently brightly colored beetles with 
a metallic luster. They fly and mate and then lay their eggs in bark 
crevices or on the outer surface of the bark, early in the spring or in 
summer. When the eggs hatch the young grubs construct long, 
winding, oval mines in either the bark or the wood, or in both (fig. 
65). These mines gradually widen as the grubs increase in size 
and end in elongated, oval pupal cells. The slender white grubs are 
the stage usually found in trees, and they can be recognized by their 
long, legless bodies, shaped like a horseshoe nail. The head is small, 
and the first segment back of the head is much broader than the fol- 
lowing body segments and has horny plates on the top and bottom. 
Growth of the larvae continues until fall, when activity ceases with 
the advent of cold weather. The winter usually is passed in the 
larval stage, although some larvae may pupate in the fall and pass 
